Armorial Families: a directory of gentlemen of coat-armour.
In its more than 1,500 pages, it covers a very large number of heraldy coats of arms in Britain, with illustrations and brief descriptions of the family histories and heads of family for each crest.
There's even a section devoted to the particular gentlemen's club to which the family head belonged.
As you may have surmised by now, the book is fully available online (for free, of course). It is a massive download, at more than 200 MB, so unless you're really keen on having this as your own file, you may want to use the Read Online ebook viewer offered at the Internet Archive. The Table of Contents can be found on page n31, while page n33 starts a list of the many splendid colored plates in the book.
Visit the main page of Free Genealogy Tools for more, umm, free genealogical tools.
And don't forget to also check for your family history at Ancestry.com and NewspaperArchive.com. These are subscription databases, but they are among the most powerful research tools available for looking into family roots.